Gene expression analysis of ubiquitin from bean under biotic and abiotic stress

A heavy metal responsive gene PvSR52 was isolated from a mercuric-chloride-treated bean (Phaseolus vulgaris L.) cDNA library by differential screening using cDNAs derived from treated and untreated plants.The PvSR52 cDNA,which contained only 281 bp,was not a full-length cDNA clone.Homology analysis of cDNA and amino acid sequence showed that PvSR52 cDNA encoded a polyubiquitin.Southern blot analysis showed that ubiquitin genes maybe encoded by a small gene family.Northern blot analysis revealed a low level of transcripts of ubiquitin in unstressed bean leaves,but the gene expressions were strongly stimulated by metals (such as Hg,Cd,As,Zn and Cu),elevated temperature,virus infection and salicylic acid.These suggested that ubiquitin proteolysis system might play important roles in resistance to various environmental stresses.